Compact Input: The State of the Art
The emergence of portable information tools such as cell phones and handheld computers has created a need for extremely compact alphanumeric input systems which are nonetheless quick and convenient to use. The systems developed fall mostly fall into three categories: character-recognition systems, binary key arrays, and permutative systems.
Character-recognition systems have the benefit of exploiting pre-existing handwriting skills. However, they are intrinsically inefficient, because the inscription of characters is an inefficient form of data input. Analyzed as a trajectory, the average letter has five critical points, each of which is an independent vector; thus inscription of a character is as physically complex as a sequence of five idealized keystrokes. As a result, handwriting speeds are about half as fast as the other systems considered here. Although once prominent in the form of Palm Computing's Graffiti™, their popularity has recently waned as people have come to appreciate that thumboards are faster and easier to use.
Binary key arrays can permit very high input rates for expert users, even in compact forms actuated by a stylus (most notably Fitaly™, from Textware Solutions, which uses a proprietary layout optimized for single-entry-point efficiency) or two thumbs (as popularized by the Blackberry™ from Research In Motion, which exploits the familiarity of the QWERTY layout). Indeed, contest results posted at the www.Fitaly.com website show speeds in excess of sixty words per minute for both of these systems. However, stylus-based systems involve the inconvenience of extracting the stylus and require two hands or a desktop, and thumboards are too large for contemporary phones. A recent thumboard—that of the Treo™ 600 (originally from Handspring Corporation and now from palmOne, Inc.)—refines the thumboard scrupulously, and achieves a width of 53 mm and a form factor which permits one-handed use. Even so, it cannot fit on contemporary cell phones. Some other recent innovations aim to sidestep the finger-width on constraint keyboard size. Levy (U.S. Pat. No. 5,973,621) uses disambiguation of multi-key strikes to permit sub-finger-width spacing. Another approach is to use fewer keys, but give each several functions; Lin et al [U.S. Pat. No. 5,528,235], for example, use five-way keys in a phone keypad. A third approach—offered on most cell phones at present and thus the most widespread binary-key solution—is dictionary-based software disambiguation, most prominently T9™ from Tegic Corporation. It provides moderately fast input for skilled users entering text, but has several drawbacks—including the cognitive noise of the system's fluctuating guesses, the need to learn an arbitrary code (the assignment of letters to numeral keys), and the need to shift to some other system for dictionary-defying data such as numbers, names and Internet addresses.
Permutative systems use codes which associate sequences of input signals with generands. For alphanumeric capacity, pair codes are sufficient. The most lucid form is what may be termed the “cellular menu”: an array of cells is displayed, each containing an array of symbols. A first directional signal selects a cell, and a second selects a symbol within the cell: a pair code is implicit in the menu. An early example is Knowlton (U.S. Pat. No. 3,967,273 1976), who describes a telephone keyboard where each button is labeled with symbols representing its neighborhood; the keyboard itself functions as a cellular menu. Millington (U.S. Pat. No. 6,256,029 2000) and Bozorgui-Nesbat (pending U.S. application 20020136371) are more recent examples. These systems, however, involve two or three taps to generate a single character, which makes them uncompetitive in speed.
An improvement is possible by using strokes across a target matrix; this fuses a pair of taps into a single fluid gesture. Furthermore, the continuity of strokes provides a natural way of transmitting a gesture-termination or parsing signal: a break in contact signals gesture completion. Liljenwall et al (U.S. Pat. No. 4,139,837 1979) and Curtin et al (U.S. Pat. No. 5,521,986 1996) both describe systems of this sort, using the end points of traced trajectories as paired vector signals. Both, however, rely on unpromising mnemonic systems based on the graphical features of characters.
A system which combines stroke gestures with a cellular menu—and then adds an efficiency-optimized layout—is described in a second pending application (#20020136372) of Bozorgui-Nesbat, and implemented in his program MessagEase™ (Exideas Inc.). It has joined Fitaly and the Treo thumboard in achieving speeds of more than sixty words per minute in the Fitaly contest; together, these three systems define the current state of the art. It is possible to foresee at least two improvements which lie ahead for them: a clamshell handset with a thumboard will keep its weight securely within the user's hand and eliminate competition for surface area between display and keyboard; and a system which combines the efficiency of Fitaly's layout with the convenience and intrinsic speed of the Treo's thumboard should be able to push the limits still further.
To summarize, several systems have shown that breakthrough performance is possible in a PDA form factor—but none of these have been successfully implemented even on the cell phones of today, with their small displays and relatively capacious front decks.
Demands of the Future
For portable devices, progress brings two compelling imperatives into collision: devices shrink, and displays expand. The scope of PDA screens increases constantly, and has now passed the VGA threshold; phones are on the same track, though a couple of years behind. As the volume required for core functionality continues to shrink, the limiting factors which prevent phones from becoming the true personal computers increasingly become display size and intolerable input systems. The full-face display is inevitable—once people are trying to read documents, watch video and browse the Internet on their phones every square centimetre of display becomes precious. A related development is the computer watch—compellingly convenient, if it ever becomes easier to use than paper.
This is the logjam the current invention addresses: shattering some assumptions which keep input from fitting wherever it is needed. First, however, some prior art on a few related topics may be mentioned:
Tentative Selection Display
                Cziernecki (U.S. Pat. No. 5,917,476 Cursor feedback text input method 1999) describes a system which uses a touch tablet as an unmarked keyboard: touching the tablet causes a character corresponding to the point of contact to be displayed, changing as the point of contact is changed; release of contact finalizes selection.        Millington also provides tentative selection display, although at the cost of an added confirmation keystroke.Input Via Non-Translational Analog Input Device        Smith (U.S. Pat. No. 5,982,203 1999) describes a permutative system marketed as Thumbscript, which uses angled trajectories. Although the marketed version has an array of binary sensors, Smith mentions use of a joystick as input device.        Macor (U.S. Pat. No. 5,901,222 1999) describes a telephone handset with a trackball or joystick in which all input is effected by activating virtual function keys.Bottom-Mounted Sensor        Bissett et al (U.S. Pat. No. 5,543,588) describe a handheld computer using a bottom-mounted touchpad. This is however a purely hardware innovation, and does not touch on data entry.        